70 INTRODUCTION TO THE STUDY OF FUNGI 



only a suspicion that the one is a form of the other. Many 

 species of PJvyllosticta growing upon living leaves, as well as 

 some species of Septoria, are supposed to be in some way 

 related to corresponding species of Zaestadia and Sphaerella, 

 but their association has never been determined. 



There is scarcely a more common mould on dead herbaceous 

 plants than Cladosporiwm herbarum, which forms dark olive 

 patches with a velvety appearance, consisting of fiexuous 

 jointed hyphae and a profusion of long elliptical conidia, at 

 first simple, and then uniseptate, proceeding from a creeping 

 mycelium. There is often to be seen, in close proximity, or 

 even mingled in the same patches, others with similar but 

 shorter threads and much larger conidia, which are broadly 

 elliptical, and not only many times septate, but the cells are 

 again divided at right angles, so as to appear muriform. This 

 is Macrosporium commune. Some have conjectured that the 

 one species passes into the other, which is hardly probable ; 

 others that there is some occult connection between them ; and 

 it has been intimated that both forms of mould are only 

 conidial states of a common Sphaeria, with coloured muriform 

 sporidia, known as Pleospora herbarum. This is another 

 example of supposed dichocarpism that rests more upon sup- 

 position than ascertained fact. 



Without indicating any particular species, it is generally 

 believed that the species of Phoma, which consist of perithecia 

 enclosing small hyaline sporules borne on short threads, and so 

 common on nearly every dead twig or herbaceous stem, are 

 each related to some ascosporous Fungus of similar appearance. 

 This is probable in at least a great number of instances, but 

 demonstrated in only a few. What are called "imperfect 

 Fungi," such as Sphaeropsideae and the Hyphomycetes, are so 

 called from the impression that they are not autonomous, but 

 simply forms or conditions of other species. Hence, if the 

 combined total of these species is accepted at eleven thousand, 

 there must be an immense number of dichocarpous species of 

 which we are still in ignorance. 



The last section of this subject includes the species which 

 produce two forms of fruit successively, or alternately, by an 

 alternation of generations. Although included here for con- 



